Photos[dot]com/Thinkstock(SHELTER COVE, Calif.) -- Five people have drowned, swept out to sea in Northern California this winter.

All five people, four from Humboldt County and one from Marin County, were pulled offshore by “sneaker waves” – the largest of a series of waves brought on by dangerous weather conditions.

"It’s one big wave in a group of other waves, so it catches people off-guard,” Pamela Boehland, a Coast Guard spokeswoman, told ABC News. “If you’re not prepared and the larger wave does come in, it can sweep you off your feet. The currents are very strong, and the water is really cold this time of year, which can take your breath away and pull you out to sea.”

The most recent victim was a 32-year-old woman who was walking on the beach with her boyfriend and dog near Shelter Cove in Humboldt County Sunday when a “sneaker wave” took them by surprise.

Earlier this month, a man and his wife went into the ocean in Marin County to rescue their dog that had been overtaken by a wave — the man was swept away.

In November, at the beginning of the particularly dangerous winter season in Northern California, a couple drowned and their teenage son disappeared while trying to rescue their dog, which had been pulled into the ocean.

“The pattern we’re seeing is that these people are out with the dogs, so we really want dog walkers to be aware and protect their pets,” Boehland said. “And if your dog does get swept away, don’t go after them. It’s dangerous, and they’re usually stronger swimmers anyway.”

In a statement, the Coast Guard warned that, especially during the winter months, Northern California beach-goers should never turn their backs to the ocean.

“This time of year, there’s a northwestern wind coming from Alaska that can cause the huge waves,” Boehland said. “Combined with erosion on beaches in low-lying areas, it puts people in a really bad position."

Boehland also said it was important for beach-goers to pay attention to advisories.

“When there is high surf advisory, just stay away from the beach,” Boehland told ABC News. “Anecdotally, it seems like there have been more of these tragedies this year than in previous years, so people need to be careful.”